The first generation of waterbeds merely consisted of large plastic bags. They were oftentimes approximately 21/2 feet deep and contained several hundred gallons of water. These waterbeds proved to be heavy enough to pose a threat to the integrity of floors on which they were disposed and to the safety of their users.
A second (and still used) generation of waterbeds utilizes a one-foot thick plastic mattress bag on a platform provided to maintain the mattress off the floor. A queen size unit of this type utilizes approximately 160 gallons of water, weighing approximately 1800 pounds.
A third generation of waterbeds, exemplified by those disclosed in U.S. Pat. No. 4,062,077 to Autrey et al. and in U.S. Pat. No. 4,015,299 to Tinnel, offer the benefits of water flotation in combination with some features of traditional mattresses. Such waterbeds consist of a mattress about six inches deep disposed on a wood base. The reduction in depth of such mattresses realizes an important saving in weight. However, the mattress can expand laterally when someone sits or lies on it. Such expansion is not only unattractive at point of sale, but the disrupting or tearing of bed coverings can result. The U.S. patent to Tinnal describes a unit wherein a mattress is circumscribed by a rigid box to prevent lateral expansion. Autrey provides a rigid circumscribing board about the water bag for that purpose. Cushions of resilient padding over and on the outside of the aforementioned rigid frameworks are employed to diminish the feel of the framework.
However, rigid peripheral units can proved to be uncomfortable in use. The rigid framework can oftentimes be felt through the resilient padding. Others in the art, such as Tinnel, use a circumscribing foam rubber periphery. However, it is difficult, in practice, to match the resiliency characteristics of the water bag with the resiliency characteristics of the foam rubber peripheral cushions. A feeling of two distinct zones in the mattress is disconcerting to users of the mattress. Moreover, foam rubber cushions tend to degrade with hard use over a long period of time.